Some pharmaceuticals need to be thoroughly mixed before they are administered to the patient. For example, crystals commonly form within liquid NPH insulin during storage. It is therefore very important that the NPH insulin be thoroughly mixed and agitated so that the crystals redissolve and/or become suspended within the aqueous component of the insulin prior to injection.
Certain medicines, in particular insulin, is generally self-administered by a patient. In some circumstances this can create psychological problems for the patient. A stigma of abnormality can be created in the mind of the insulin patient when conventional syringes must be used to administer the insulin.